Coating process and apparatus

ABSTRACT

This invention provides an apparatus and process for automatically coating solid pharmaceutical dosage forms, e.g., tablets. The apparatus comprises a coating pan, having a rotating means, e.g., motor and a weighing means, e.g., scales in combination with the pan and motor. A process controller is in electronic communication with both the pan motor and scales, for controlling the pan rotation and monitoring the weight of the coating pan contents. There is also provided a plurality of material containing reservoirs having conduit means communicating with the interior of the pan. The material containing reservoirs may also have weighing means, e.g., scales in combination with the reservoirs, which are also in electronic communication with the process controller. These reservoirs may contain a water supply, a coating syrup supply, color suspension supply, and polishing ingredients for use in coating the tablets. The process controller is pre-programmed to dispense the various coating ingredients in a precise sequence, while monitoring the coating weight of the tablets, whereby the entire coating process is automatically effectuated in one continuous operation.

This is a division of application Ser. No. 613,962, filed May 24, 1984now abandoned, which in turn is a division of Ser. No. 489,044, filedApr. 27, 1983, now abandoned, which in turn is a division of Ser. No.304,100, filed Sept. 21, 1981, now U.S. Pat. No. 4,407,844, which inturn is a division of Ser. No. 140,469, filed Apr. 17, 1980, now U.S.Pat. No. 4,310,562, which in turn is a division of Ser. No. 934,519,filed Aug. 17, 1978, now abandoned, which in turn is a division of Ser.No. 777,468, filed Mar. 14, 1977, now U.S. Pat. No. 4,133,290, which inturn is a continuation-in-part of Ser. No. 672,766, filed Apr. 1, 1976,now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to coating of solid pharmaceutical dosage forms.More particularly, it relates to an automatic, continuous coating ofsolid pharmaceutical dosage forms.

In the prior art coating of solid pharmaceutical dosage forms, e.g.,tablets, many of the coating steps require introduction of manual labor.These prior art coating processes also are relatively imprecise in theamounts of ingredients that are placed upon the tablets, causingvariations in finished tablets.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a coating apparatus of thisinvention;

FIG. 2 is a cross-sectional view of a spray nozzle of this invention.

FIG. 3 is an isometric view of dispursing means of a coating apparatusof this invention; and

FIG. 4 is an isometric view of the front of a coating pan of a coatingapparatus of this invention.

SUMMARY OF THE INVENTION

Broadly, this invention provides an apparatus for automatic andcontinuous coating of solid pharmaceutical dosage forms, e.g., tablets,and comprises a container means, e.g., coating pan, in rotatablecommunication with a rotating means, e.g., motor, with both the coatingpan and the motor in operative relation to a weighing means, e.g.,scale. Preferably the coating pan rests upon the motor and is rotated byit about the horizontal axis of the pan, with both pan and motor restingupon one or more scales.

One or more material reservoirs are provided which have conduit means influid communication with the interior of the coating pan. Flow controlmeans, e.g., a valve or pump are provided for the control of the flow ofthe material in the reservoir through the conduit means into theinterior of the coating pan.

A process controller means which is in independent electroniccommunication with each of the motor, scale, valve and/or pump, controlsthe rotation of the coating pan and the flow of material from thereservoir in a preprogrammed sequence, based upon the changing weight ofthe tablets and coating material in the coating pan.

In a preferred embodiment of the invention at least one of the materialreservoirs are in operative relation to a reservoir weighing means,e.g., scale, for continuously determining the weight of the material inthe reservoir, with the scale in electronic communication with theprocess controller means, for continuous monitoring of the weight of thematerial in the reservoir.

In a further preferred embodiment of this invention, one or more of thematerial reservoir conduits may have one or more nozzles for introducingmaterial from the reservoir into the interior of the coating pan. Thenozzle comprises a fluid outlet port in fluid communication with thereservoir conduit, a circumferencial air chamber about the fluid outletport with the air chamber having an air inlet. The fluid outlet port hasan extendable portion beyond the air chamber with an elastomeric cap innormally air tight engagement with the extended portion. A fasteningmeans, e.g., locking nut holds the cap in air-liquid sealed engagementwith the end of the air chamber.

The apparatus also provides an air supply means and air exhaust means influid communication with the interior of the coating pan; both the airsupply means and the air exhaust means are in electronic communicationwith the process controller means.

The apparatus is preferably supplied with a heating means, temperatureregulating means and filtering means for the air supply means. The airsupply means and the air exhaust means are also provided with air flowregulating means.

There is also provided an alarm means for the process controller means,whereby malfunctions in the process are automatically brought to theoperator's attention, and whereby the apparatus is automatically shutdown.

While it is within the scope of the invention that some of the reservoirmeans may have a common pump, it is preferred that each reservoir with apump means have an individual pump.

It is also within the scope of the invention that the materials in thereservoirs may be transferred into the coating pan by means of meteringpumps actuated by the process controller means without the necessity ofmonitoring the weight of the material in the reservoir.

In the operation of the automatic coating apparatus, the processcontroller, prior to each cycle senses the weight of the tablets in thecoating pan (via the scale) and applies the required amount of coatingmaterial to the tablets in the sequence programmed. Based on the weightreading of tablets plus the coating pan, the process controllercalculates how much material to add for each cycle to attain a specificrequired weight. A base coating, medium coating, and color coating areapplied as solutions or dispersions. The weight of these liquids in thereservoirs are monitored by the process controller and the requiredamount is delivered to the tablets in the coating pan upon a signal fromthe process controller. Alternately, the liquids may be dispersed fromthe reservoirs by metering pumps upon a signal from the processcontroller means, without monitoring the weight of the liquids.

In a given sequence, a plurality of tablets are charged into the coatingpan and the weight of the pan and tablets recorded in the processcontroller. The exact amount of coating liquid or pigment dispersion tobe added is determined by the process controller, based on readings ofthe weight of the pan and tablets. The amount is calculated such thatthe specified weight of the final tablet is obtained regardless ofvariations in the density of the coating liquids or pigment dispersionsor other factors. The coating liquid or pigment dispersions are added byweight of the liquid.

The process controller is actuated to effect and execute the individualsteps of the process. The pan is rotated to tumble the tablets while abase coating is applied to the tumbling tablets as a series ofindividual coatings in the presence of drying air. After the basecoating has been applied, the tablets may be additionally air dried.Following the drying cycle, a medium coating is applied as a series ofindividual coatings with air drying of each coating after an adequatetablet tumbling time. The interior surfaces of the pan are automaticallycleaned and/or kept smooth by transferring adhered coating material fromthe pan walls to the tablets. The process then proceeds to the next stepof coloring the tablets by the process controller actuating the rotationof the coating pan to tumble the tablets while a series of pigmentdispersion coatings is applied to the tablets with air drying of thecolored tablets after each application The automatic cleaning of theinterior surfaces of the pan may also be done during and after colorcoating. The tablets are automatically pre-polished after coloring byadding small amounts of pigment dispersion and first continuous, thenintermittent tumbling of the tablets for a selected period of time inthe absence of drying air, and then polished by continuously tumblingthe tablets while applying a polishing material on the tablets. At theend of the polishing stage, the process is stopped and the tablets maybe removed from the coating pan.

In a preferred embodiment of this invention, the pan walls may be cooledexternally by blowing cold air and/or spraying a first mist of waterover the outside of the pan during part of or during the entire basecoat and medium coat and color applications. By cooling sufficiently,any build-up of coating material on the pan may be eliminated.

In another embodiment of this invention, the pan may be kept clean byspraying water on the inside of the pan wall after the syrupapplication, while the drying air flow is reduced, or turned offcompletely. The relatively high humidity resulting inside the pansoftens the build-up on the pan and transfers it onto the tablets.Sections of the pan where build-up of the coating materials is moreintense, may be sprayed more frequently.

In still another embodiment of this invention, a combination of coolingthe pan and spraying water on the interior surface may be used toprevent coating material build-up.

Additionally, before each medium coat application, a fine mist of wateris applied to the interior of the pan surface. The fine water mist isbelieved to dissolve some of the material built up on the tablets andtransfer this as a thin film to the pan interior surface giving thetablets enough grip to tumble over the smooth pan surface rather thanslide upon it.

In a clean pan, the tablets slide rather than tumble, which has anegative effect on weight distribution and shape of the tablets. To givethe pan a very slight roughness, just enough to keep the tabletstumbling for the duration of liquid addition, a fine mist of water issprayed on the interior surface of the pan approximately 10 to 30seconds before the liquid addition. This spraying has little or noeffect on the formation of material build-up since at the time ofspraying the dry air flow is turned on full and the humidity inside thepan is low.

In each of the steps of base coating, medium coating, coloring,pre-polishing, and polishing, the materials required are automaticallysupplied to the tablets in a precise sequence and in the requiredquantities.

In the operation of the apparatus of this invention, the drying air maybe delivered to a 300 kg. capacity coating pan at about 600 to 800 cubicfeet per minute (CFM), (full air flow), and at a temperature of fromambient temperature to 70° C.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Referring now to FIG. 1, the apparatus of this invention is showngenerally at 10. It comprises a coating pan 11, rotatable about itshorizontal axis, a motor 12, for rotating the pan 11, load cells, e.g.,scales 13. Preferably the pan motor 12 which supports and rotates thecoating pan 11, rests upon the scales 13. Both the motor 12 and the loadcells 13 are in electronic communication with a process controller 14,via circuits 16 and 17. The apparatus is also provided with materialreservoirs 18, 19, 21, and 22. Reservoir 18 may be a pressurizedpurified water supply, reservoir 19 may contain a coating fluid, e.g.,talc syrup, for use in the base coating and medium coating, reservoir 21may contain another coating fluid, e.g., a color solution or dispersion,for the color coating of tablets; and reservoir 22 may contain apolishing wax, e.g., carnauba wax powder, for polishing tablets. Each ofthe reservoirs 19 and 21 is provided with a conventional liquid pumpmeans 24 and 26. Reservoir 18 is provided with a conventional liquidvalve 23 and reservoir 22 is provided with an air supply controlled by aconventional pneumatic valve 27. Each of valve 23 and the pumps 24 and26 are in fluidic communication with the interior of the pan 11, viaconduits 28, 29 and 31. Reservoir 22 is in fluidic communication withthe interior of pan 11, via conduit 32. The valve and pumps 23, 24, 26,and 27 are in electronic communication with the process controller 14,via circuits 33, 34, 36, and 37. The reservoirs 19 and 21 are preferablysuspended from a load cell, e.g., scale 38, which load cell is inelectronic communication with the process controller 14, via circuit 39.

FIG. 2 depicts the reservoir conduits 28, 29, 31, and 32 entering therear of the coating pan 11. A housing 30 (shown in phantom in FIG. 3)may be used to cover these conduits with the end of the conduitsprotruding from the housing 30 into the pan 11. Conduits 29 and 31 areequipted with nozzles 66 which are more fully described further on.

The apparatus is further provided with an air supply means 41, which airsupply has a heater means 42, a filter means 43, a temperaturecontroller 44 and a blower means 45. The temperature of the heater 42 iscontrolled by the temperature controller 44, via circuit 46. Thetemperature controller is in electronic communication with the processcontroller, via circuit 47. The air supply means 41 is in communicationwith the interior of the coating pan 11, via conduit 48. The apparatusis also supplied with air and/or water cooling means 50, for cooling theoutside surface of the pan 11.

The apparatus is also supplied with exhaust means for exhausting thecoating pan 11, and it comprises a blower 49 and a filter 51. The bloweris in communication with the interior of the coating pan 11, via aconduit 52.

The air supply means and the exhaust means are each provided with flowcontrol valves which allow for three levels of control (1) cut off (noair), (2) reduced air flow, and (3) full air flow. Reduced air flow isapproximately one-third of full air flow.

As shown in FIG. 3 conduits 48 and 52 may be located within the housing30. The air flow from conduit 48 into the pan 11 is via air vents 55.The pan 11 is exhausted via exhaust vent 55a, which may be covered witha screen on the housing 30 opening.

The electronic communication of circuits 17 and 39 with the processcontroller is, via an electronic scale 53, which scale is integratedinto the process controller.

The process controller is provided with a readout means 54, which may beof the type well known in the art, such as an alphanumeric read-out. Thecontroller is further provided with a program-selector 56 andbatch-weight selector 57 for automatic compensation for batch weightvariations. An alarm system 58 is provided for the detecting ofabnormalities in the process and a manual controller 59 which overridesthe process controller is also provided.

The coating pan 11 is also provided with seals 61 and 62 on the openings63 and 64. These seals may be in the form of pannels, such as metal orplexiglass. Seal 62 is provided with openings for the various conduitsentering the pan 11 interior. The coating pan 11 may be convenientlycharged through a removable seal 61.

In an additional preferred embodiment of this invention, the conduits 29and 31 are provided with one or more nozzles 66 illustrated in FIG. 4.While each conduit 29 and 31 may contain one or a plurality of nozzles66, a description of one nozzle will be sufficient to illustrate theembodiment.

The nozzle 66 is detachably mounted in fluid tight relationship (notshown) on either or both of conduits 29 and 31 by conventional means,e.g., locking nut. The nozzle 66 comprises a fluid outlet port 67 fordisbursing the coating fluids. Circumferential about port 67 is an airchamber 68, having an air inlet port 69. (The air supply for port 69 maybe the same as for valve 27 or may be an independent source.) The fluidoutlet port 67 extends beyond the air chamber 68. The portion of theport 67 extending beyond the air chamber 68 is in normally airtightengagement with a center bore 77 of a spray cap 72. The cap 72 comprisesa generally V-shaped wedge-like tip 76 at its distal end. At theproximal end of the bore 77, the bore flares conically. The cap 72 isheld in air-fluid tight engagement against the end 79 of the air chamber68 by a locking nut 81.

The cap 72 is made of an elastermeric material, e.g., silicon rubber andhas on the apex of the V-shaped tip 76 a normally closed expandableapperature 82.

The coating liquid inlet port 67 may also be provided with a check valve70 which is similar to the spray cap 72. The check valve 70 prevents anyback flow of air into conduit 67 when cleaning or purging the nozzlewith air.

In operation, coating fluids are pumped via conduits 29 and 31 into theport 67. Simultaneously, air under pressure from the air inlet port 69enters the air chamber 68. The air then enters the conical area at theproximal end of the bore 77 and is forced along the normally closed bore77 expanding it to reach the apperature 82. The air and/or liquidpressure forces open the normally closed apperature 82, allowing the airand coating fluids to enter the pan 11 as an atomized spray. When theliquid addition is completed, reduced pressure in the tip allows theapperature 82 to close.

The spray nozzle 66 may also be operated without air pressure from theair inlet port 69, when so used, the coating fluids enter the pan 11 asa stream and are poured on the tablets.

The spray nozzle described prevents the coating fluids from dripping,drying out, and/or clogging the conduits 29 and 31, and air inlet port69.

In another embodiment of this invention, the coating pan 11 may beequipped with baffels 40 (See FIG. 3) on its internal surface. Thesebaffels 40 may be hollow and contain a heat transfer liquid, e.g.,water, which acts as a heat exchanger to help maintain the temperatureof the coating pan at the desired temperature. These baffels 40 may alsoact in conjunction with the external pan cooling means 50 to maintainthe desired pan surface temperature.

In a further embodiment of this invention, the load cell 38 iseliminated and each of the pump means 24 and 26 are metering pumps. Inoperation the process controller 14 dispenses the liquids in reservoirs19 and 21 by actuating the metering pumps 24 and 26. All other aspectsof the invention are as described above.

While the apparatus of this invention has been described in relation tosyrup coating, nevertheless, the apparatus may also be used for filmcoating of tablets, wherein a film, e.g., polymeric film is applied tothe tablets. When so operated normally only the load cell 38 and onereservoir 19 or 21 is used to dispense the film coating solution. Thepan load cell 13 is not in operation. The desired weight amount of filmcoating solution is automatically dispensed by the process controller 14from reservoir 19 or 21, via conduits 29 or 31 respectivley, and appliedto the tablets, until the desired film coat weight is achieved. The airflow and exhaust system are actuated during the film coating process.Nozzle 66 is used in its atomized spray mode.

The operation of the apparatus of this invention will be understood fromthe following example, wherein tablet cores are automatically syrupcoated.

EXAMPLE

One hundred-seventy kilos of tablets (approximately 1.1 million tablets)are charged into a 300 kilogram Pelligrini coating pan 11. The processcontroller 14 is actuated after having pre-selected the batch weight andthe coating procedure to be followed for the particular tablets to becoated. The tablets to be coated each have a 160 milligram core of which25 milligrams is MELLARIL (thioridazine HCl, Sandoz, Inc. Hanover,N.J.).

The controller is actuated and the following coating steps affectuatedwith the process controller 14 monitoring the weight of the tablets inthe coating pan 11 prior to each liquid addition, and comparing thatweight to what the tablets should weigh at that point in the tabletingprocess; and if necessary, adjusting the dispersing of the liquidaccordingly.

Step 1--The tablets are base coated by addition of one kilogram of talcsyrup from the talc syrup reservoir 19. This amount of syrup is addedeight times to the rotating coating pan to produce eight coats on thetablet core. It is added at intervals of 5 minutes in the presence of70° C. air at 600 to 800 CFM air flow.

Step 2--A medium coating of approximately three kilos of talc syrup perapplication is applied as 32 coats to the tumbling tablets from the talcsyrup reservoir 19. Each talc syrup application is applied at thebeginning of a 12-minute cycle. For the first 21/2 minutes of the cycle,there is no air flow. From 21/2 minutes until 6 minutes this is reducedair flow, and from 6 minutes to 12 minutes there is full air flow. Theair flow is at a temperature of 70° C. Additionally, 30 seconds beforeeach medium coat application a fine mist of water is applied to theinterior of the pan wall. The cooling blower is turned on at thebeginning of each cycle and turned off as soon as the full air flow isturned on.

Step 3--The base and medium coated tablets are color coated bydispensing from reservoir 21, a dispersion of a pigment in a sucrosesolution. This color dispersion is supplied in 30 cycles, with eachcycle containing 900 to 1000 grams of the solution. Each cycle has thefollowing sequence:

Addition of color dispersion 1.5 minutes tumbling without air, 2 minutestumbling with reduced air flow, and 3.5 minutes of full air drying atfrom ambient temperature to 60° C., for a total of seven minutes percycle.

Step 4--This is a pre-polishing step, which is divided into two parts.The first part consists of one to four applications of 0.5 kilos ofcolor dispersion. The applications are applied at intervals of sevenminutes without the presence of drying air. The second part of thepre-polishing step is a jogging cycle without the presence of dryingair, wherein the pan is rotated, e.g., tablets tumbled, for threeseconds every two minutes. This is repeated for ten cycles; at whichtime the tablets are tumbled for three seconds every five minutes andthis is repeated for ten cycles.

Step 5--The tablets are polished by blowing, via conduit 27, 50 grams ofcarnauba wax over the tablets within a twenty second period. The tabletsare then continuously tumbled for 45 minutes without drying air. At theend of the tumbling period, the coated, colored, and polished tabletsare removed from the coating pan.

What is claimed is:
 1. In an apparatus for coating solid pharmaceuticaldosage forms having coating means in association with a container meanswhich is in rotatable communication with a rotating means, theimprovement which comprises means for applying a fine mist of water tothe interior of the coating pan wall.
 2. In an apparatus for coatingsolid pharmaceutical dosage forms having coating means in associationwith a container means which is in rotatable communication with arotating means, the improvement which comprises cooling means forcooling the external surface of the container, and means for applying afine mist of water to the interior of the coating pan wall.
 3. Theapparatus according to claim 2 wherein the cooling means is a blowingmeans for conducting cooling air over the external surface of thecontainer means.
 4. The apparatus according to claim 2 wherein thecooling means is spraying means for applying cooling water over theexternal surface of the container means.